Mechanical AWS Sunflower Patch

The Automatic Warning System (AWS) has been in use on British railways since the mid 20th century and is one of the world’s more simple railway safety systems. On approaching an restrictive signal state – in the UK a double yellow, single yellow or red – or significant speed reduction trackside magnets activate an audible warning in the cab the driver must acknowledge within several seconds with failure to do so activating the train’s emergency brakes. Once the alert has been acknowledged a visual reminder, the AWS ‘sunflower’, is displayed. On approaching a clear signal a tone is played and any previously activated visual display cleared. Early systems used air horns, bells and mechanical ‘sunflowers’; modern systems use beeps and digital displays.